1. Field of the Invention
The present invention relates generally to an optical mechanism with indexing stage with at least one fixed diameter apodized aperture and methods of making same.
2. Description of Related Art
Since essentially the advent of photography adjustable camera settings have been critical in obtaining correctly exposed pictures. These adjustments include “shutter speed” (adjustable exposure time of the “film”), “film speed” (choice of film sensitivity), and lens aperture (adjustable diaphragm in the lens). In addition to affecting the film exposure, these adjustments also provide other essential benefits. For example, the shutter speed adjustment allows the photographer to freeze in time a fast moving scene. The film speed allows the photographer to get the desired grain in the image. The lens aperture adjustment allows the photographer to get the desired depth of field.
In digital cameras, the electronic shutter control (adjustable integration time of the image sensor) often replaces the mechanical shutter but does not eliminate the need for the lens aperture adjustment which remains an indispensable tool, not only to control the amount of light impinging on the imaging sensor but also to achieve the desired depth of field in the associated image.
One common form of lens aperture adjustment for digital cameras is the mechanical iris diaphragm or mechanical iris. The mechanical iris consists of multiple blades which can be moved with respect to each other so as to form an adjustable pseudo-circular polygonal aperture. The blades are often attached to an inner ring and an outer ring moved relative to each other to adjust the mechanical iris. Most film cameras and many digital cameras incorporate a mechanical iris or some other form of lens aperture adjustment (e.g., a rudimentary aperture wheel).
However, there are some notable exceptions: disposable film cameras, very-low-cost digital cameras and many cell phones. The main reason for not using a lens aperture adjustment in these areas is cost. For example, an inexpensive mechanical irise design can be a reasonable component of a digital camera costing possibly less than ½ of 1% of retail price of the total camera unit, but this same inexpensive iris component may cost more than ⅓ of the retail price of a disposable camera or more than ⅓ of the cost of a camera module intended for computer or cellular telephone applications. Thus almost all cell phone cameras (also referred to as cell phone camera modules) do not include a lens aperture adjustment.
Cell phone cameras were, originally, not designed as replacements for traditional cameras. Cell phone camera modules were supposed to produce acceptable images in dim fight conditions without a flash. For this reason, they were fitted with lenses with a large fixed aperture (e.g., f/2.8) to maximize sensitivity at the expense of the depth of field), and relied on the electronic shutter to adjust the exposure level. Consequently these cell phone cameras with no aperture adjustment produce questionable quality images at low-light level due to objectionable shot noise and readout noise and at high-light level due to poor depth of field and reduced sharpness due to lens aberrations.
However due to their enormous popularity (already outselling film and digital cameras), cell phone camera modules are now poised to replace traditional cameras. As a point of reference on popularity, at the end of 2010 there were over 5.3 billion mobile cell phone subscriptions worldwide or over ¾ of the world population, with the Americas listing 880 million subscriptions and Europe listing 740 million subscriptions. Regarding use of cell phone cameras, according to a December 2010 study 52.7% of mobile users in the United States, 57.5% in Europe and 62.9% in Japan used their mobile cellular devices for taking photographs.
Cell phone camera modules need to approach or match traditional camera image quality at a fraction of the cost of a traditional camera. This issue is further aggravated by price pressure and market demand for a larger number of pixels. As semiconductor technology progresses, image sensors get sharper and pixels get smaller thus requiring a lens with a wider aperture in order to maintain the same sensitivity. This requirement conflicts with the need for a sharper lens (since a wider aperture results in greater lens aberrations) and for an increased depth of field (since a wider aperture results in a reduced depth of field).
Two solutions that have attempted to improve cell phone camera modules are the optical auto-focus using a “liquid lens” and the “phase-mask” approach using image processing algorithms. In the case of the optical auto-focus using a liquid lens, the depth of field is not increased. Rather, the focus is simply adjusted for a particular distance. In the case of the phase-mask approach, the focus of the lens is in fact degraded. A phase-mask (placed on one of the lens elements) introduces a relatively constant amount of defocus throughout an extended depth of field. The sharpness is then partially restored by digitally using image processing algorithms. Unfortunately, the sharpness restoration algorithms also introduce a significant amount of noise in the image.
It is clear that none of these solutions really eliminate the need for an inexpensive adjustable lens aperture but there are no suitable technical implementations fulfilling this need for cell phone camera modules. Current mechanical irises are too expensive, too bulky, too fragile, and too power-hungry to satisfy the expected one-billion cell phone camera module market. Mechanical irises also have another serious technical drawback that diffraction through their circular aperture significantly degrades the image sharpness for small aperture settings, e.g., high f numbers such as f/5.6 or higher.
An apodized aperture greatly reduces the detrimental diffraction effects at small aperture sizes (high f numbers such as F/7+) by minimizing sharp edges that cause the diffraction. Others have noted advantages to apodized apertures at larger aperture sizes (F2.8 and above). Apodized apertures become increasingly advantageous as optical sensor pixel density or number increases and/or pixel size decreases.
There have been several proposals in the patent literature that attempt to address these deficiencies such as U.S. Pat. No. 7,585,122, which is incorporated herein by reference, which discloses an electro-mechanical adjustable aperture camera for cell phone applications and the like that is formed of at least two electrodes, and an electrical circuit for applying a voltage to the electrodes in order to create an electric field between the electrodes. U.S. Pat. No. 7,929,220, which is incorporated herein by reference, discloses an adjustable apodized lens aperture constructed using photochromic material. U.S. Pat. No. 6,621,616, which is incorporated herein by reference, discloses certain embodiments providing an electrochromic element for a camera that could be used as a shutter, variable light transmittance filter, and iris simultaneously. U.S. Published Patent Application Serial Number 2010-0134866, which is incorporated herein by reference, teaches the broad concept of an optical element with an electrochromic apodized aperture having variable light transmittance in response to the amplitude of an applied voltage. The broad electrochromic apodized aperture solutions of the prior art such as particularly disclosed in U.S. Pat. No. 6,621,616 and/or U.S. Published Patent Application Serial Number 2010-0134866 may not, due to complexity, be implemented in a manner that is cost effective for efficient large scale manufacturing.
In addition to cost issues there is a need for durability in a cell phone environment as cell phones typically undergo significantly more abuse than conventional digital or film cameras. Thus there is a need for a certain rugged durability in designs intended for cell phone implementation.
There remains a need for cost effective, durable, rugged mechanism for varying the aperture of cameras, such as found in cell phones It is an object of the present invention to develop optical elements incorporating the ability to provide distinct apodized apertures for a camera aperture, and methods of making the same suitable for efficient, effective manufacturing for incorporation into inexpensive camera units such as cell phones.